Vulcanization of rubber



Patented July 11, 1950 VULCANIZATION OF RUBBER Albert F. Hardman, Akron, Ohio, assignor to Wingfoot Corporation, Akron, Ohio, a corporation of Delaware No Drawing. Continuation of application Serial N 0. 508,405, October 30, 1943. This application September 1'7, 1945, Serial No. 616,967

2 (Hanna (Cl- 260785) This invention relates to the vulcanization rubber with amino esters of dithiocarboxylicacids. These new compounds and methods of preparing them are claimed in my copending; application Serial No. 508,403, filed October 30, 1943, now abandoned.

The new compounds are prepared by reacting ammonia or an amine with formaldehyde and a dithiocarboxylic acid. The amine may contain one or more nitrogen groups, and the nitrogen groups may be separated by an aliphatic or aromatic radical, such as ethylene, propylene, phenylene, naphthylene, diphenyl, etc.

The dithiocarboxylic acids useful in the invention are those acids in which the dithio acid roup is directly connected to a carbon of the acid residue as, for example, dithiofuroic acid; the dithionaphthoic acids, inQlilding the hydroxysubstituted compounds, such, as 2Fhydroxye1- dithionaphthoic' acid and l -hydroxy-2-dithionaphthoic acid, etc; dithiobenzoio'acid; dithioe acetic acid; etc.

The accelerators of this; inventionmay be produced from'the methylol estersof the dithiocarboxylic acids which can beprepared as follows:

EXAMPLE A M ethylol dithiofuroate Ammonium dithicfuroate in 150 cc. water g 16 Concentrated HCl g 11 Formaldehyde .(37%) g Water and ice cc 200 The aqueou ammonium dithiofuroate was slowly stirred into a mixtureof the hydrochloric acid, formaldehyde, Water, and ice. In a few minutes crystals separated. After standing onehalf hour, the crystals were filtered off and washed with cold water. These crystals were methylol dithioiuroate. M. P. 40 C.

EXAMPLE B Crude disodium-Z-hydroxy-l-dithionaphthoate in 200 cc. water g 35 Concentrated HCl cc 20 Formaldehyde (37%) g.. 15 Water cc 400 Orange-colored EXAMPLE 1 IJiethylol. 2 hydroxy l-dithionaphthoate" g' 25 Alcohol -1 cc 1.00 Aniline. g 11;

01 adding the aniline, the solution became warm, and in a short time crystals separated.

These melted at 116 C.

EXAMPLE 2 Methylo1-2-OH-l-dithionaphthoate g 25 Alcohol "no cc Cyclohexyl amine g 10 The mixture became warm and-crystals separated almost immediately. The-crystals melted with decomposition at 122-123" C.

EXAMPLE 3 N,N'-diphenyl-p-phenylene-diamine g 13 Acetone r cc Methylol 2 hydroxy l dithionaphthoate The solution was allowed to stand for 2 hoursat room temperature, then stirred rapidly. Crysr talsbegan to separate. After 24 hours at room temperature,- light orange-colored crystals were, obtained, melting after recrystallization from acetone at-193 C.

Analysis: Sulfur found, 17.83 and 18.05 per cent; nitrogen found, 4.00 and 4.07 per cent.

Calculated to formula below: Sulfur, 17.70 per cent; nitrogen, 3.87 per cent.

H H CSC 0-5-0 11 H\ /H 11 OH S /N N\ S OH EXAMPLE 4 Methylol dithiofuroate g 17.5 Alcohol cc Aniline g 10 Stirred aniline into solution of methylol dithiofuroate slowly, with cooling. A thick suspension of orange-colored crystals quickly formed. The melting point of the product was 97 C.

Analysis: Sulfur found, 26.45 and 26.53 per cent; nitrogen found, 5.46 and .54 per cent.

Caculated to anilinomethyl dithiofuroate: Sulfur, 25.70 per cent; nitrogen, 5.62 per cent.

EXAMPLE 5 i N,N-diphenyl-p-phenylene diamine g 13 Acetone cc 100 Methylol dithiofuroate g 19 Allowed solution to stand at room temperature, 3 hours, until crystals began to separate. then stirred rapidly. After 25 hours, a good yield of crystals was collected. After washing with acetone, these melted at. 147 C.

Analysis: Sulfur found, 22.53 and 22.78 per cent; nitrogen found, 4.88 and 4.88 per cent.

Calculated to N,N-diphenyl-p-phenylene-diamino-N,N'-bis-methylene dithiofuroate: Sulfur, 22.40 per cent; nitrogen, 4.88 per cent.

EXALlPLE 6 hot Methylol dithiofuroate g 20 Benzene cc 100 Concentrated NH4OH (28%) g 4 Stirred the mixture rapidly. Heat was evolved and red crystals soon began to separate. The reaction mixture was allowed to stand 3 days at room temperature, then filtered, and washed with benzene. M. P. 114 0.

Analysis: Sulfur found, 39.02 and 39.33 per cent; nitrogen found, 2.87 and 2.87 per cent.

,Calculated to amino-trimethylene dithiofuroate: Sulfur, 39.60 per cent; nitrogen, 2.89 per cent.

The structural formula is:

of vulcanization is illustrated by the following examples. The accelerators of Examples 1 and 2 were compounded with natural rubber according to the following formula:

Natural rubber 100.0 Sulfur 3.0 Zinc oxide 5.0

Accelerator V 0.5

V, The eficacy of the compounds as accelerators 4 After vulcanizing 20 minutes at 240 0., they gave the following test results:

Example No. f i Elongation gg rF KgJsq. cm. Per Cent In addition to natural rubber, various synthetic rubber-likematerials (such as rubber-like copolymers of butadiene-1,3 with other monomers, such as styrene, acrylonitrile, etc.) which are'similarly vulcanizable, may also be used and, for the purposes of this invention, are to be considered to be equivalents of natural rubber. To illustrate this, other esters were compounded with GR-S according to the following formula:

GR-S' 100.0 Sulfur 2.0

Zinc oxide 5.0 Carbon black 40.0 Accelerator 1.0

On curing as indicated, they gave the following test results:

Example No. Cure I gg gi Elongation Mgaioi lylaus D8976 ll-l q. 0111. Per Cent -2. Rubber vulcanized in the presence of sulfur I and an aminomethyl ester of dithiofuroic acid.

' ALBERT F. HARDMAN.

No references cited. 

1. THE PROCESS OF ACCELERATING THE VULCANIZATION OF NATURAL RUBBER WHICH COMPRISES CURING THE SAME IN THE PRESENCE OF SULFUR AND AN AMINOMETHYLESTER OF DITHIOFUROIC ACID. 